NET INCOME PER SHARE - Schedule of Calculations of Basic and Diluted Net Income per Share and Potential Common Shares (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2013
Numerator:
Net income	$ 20,854	$ 17,629	$ 11,233	$ 11,476	$ 16,676	$ 17,294	$ 9,883	$ 5,253	$ 61,192	$ 49,106	$ 40,609
Weighted Average Number of Shares Outstanding, Basic [Abstract]
Denominator for basic net income per share - weighted average common shares outstanding (in shares)									41,105	41,366	41,665
Dilutive common equivalent shares:
Weighted average stock options (in shares)									9	54	122
Weighted average restricted stock units (in shares)									523	535	535
Denominator for diluted net income per share - weighted average shares outstanding (in shares)									41,637	41,955	42,322
Net income per share:
Basic net income per share (in dollars per share)									$ 1.49	$ 1.19	$ 0.97
Diluted net income per share (in dollars per share)	$ 0.50	$ 0.42	$ 0.27	$ 0.27	$ 0.40	$ 0.41	$ 0.24	$ 0.12	$ 1.47	$ 1.17	$ 0.96